Engine speed control system



Dec. 2, 1.941.

B. O. AUSTIN ETAL ENGINE SPEED CONTROL SYSTEM Filed Jan. 24, 1940 Fzy z.

R. RM. 400 600 J200 1600 2000 by meld/:by Jpc ed Hmps.

INVENTORS ascum 0- Huz and Patented Dec. 2, 1941 i0.. Austin, Forest Hills, and Clarence A. Atwell, Wilkinsbm'g, Pa., assigner! to Westing- .house Electric & .Manufacturing Company, East .Pittsburgh Pa., a corporation of Pennsylvaliia Application January24, 1940, Serial N0. 315,374

,'9 Claims.

Our invention relates generally to con-'trol systems, and more particularly, to Asystems 'for foontrolling the operation vof 'Diesel or gas-electric vehicles.

In view of tl'ie inherent characteristics of electric generators .of the type utilized `for ysupplying current to `the motors of Diesel or gas-electric vehicles, the engine, which drives the generator, overspeeds at low currents vand the Aengine speed is held down too much at medium currents. However, the `generator unloads and the engine `overspeeds at lhlg'h currents. The unloading of the generator `results 'from the armature 'reaction and increased resistance :drop at high currents which lowers the generator voltage, :thereby reducing the kilowatt output ofthe .generator :and per/mitting the engine to :overspeed One object 'oi' `our invention, generally stated, is to provide 'for holding the engine speed approximately constant throughout the -operating range of ran engine driven equipment.

A more specific object of our invention 'is 'to regulate the speed of an .engine which drives a generator bycontrolling the excitation of the generator.

Another object .of our invention iis to utilize operating characteristics =of an engine 4driven igenerator for regulating the speed of the engine.

Other yobjects will be explained ".fully hereinafter or will be apparent to those skilled inthe art.

.According to our invention, the engine speed is regulated by controlling lthe ygenerator excitation by means of a rplurality of relays responsive to either the generator current Ior the generator voltage. The lrelays are Vset :to operate in .a predetermined seque'n'ce to vary the :generator 'excitation, thereby controlling the load on the Aengine to regulate the engine speed.

For a fuller understanding of the nature and objects of the invention, reference may l.be had to the following detailed! description, taken in conjunction with the accompanying drawing, in which:

Figure 1 is ya diagrammatic view of 1a Icon-trol system embodying our invention;

Fig. 2 is a diagrammatic view of a modification .of the invention, `and Figs. 3 and 4 are .curves showing operating characteristics vof the machines illustrated in Figs. 1 and 2.

Referring to the drawing, and particularly to Fig. 1, the system shown therein comprises a motor l0, fa generator H for supplying current to the motor and an internal combustion engine I2 for driving the Vgenerator H.. "The motor Ill is preferably of the series type suitable 'for propelling a bus or -othervehi'cle .and .is providedwlth a series eld winding 'I3 and a reversing switch I4 for reversing the dinectionof .rotation inthe usual manner. The v:generator il .is provided 'with .a shunt :ileld winding l 5 'which .-i's normally energized by the generator.

1n order to cause the generator potential to build up quickly when vthe engine is accelerated, a battery `lili is connected inthe circuit for the field winding lft by means Iof a switch l'l which may be operated *in conjunction `with the accelerator .or throttle for the engine l2. When the generator .potenti-ai reaches a predetermined Value, a relay Vis-operated todisconnect the battery .It Vfrom the :eld winding i5. A variable rh'eostat Hl maybe 'utilized `to adjust the current supplied to the ield winding .l5 by the 'battery i6.

As explained hereinbefore and illustrated by the engine 'operating curves shown in Fig. 3, the engine overspeeds at light .loads 'and the speed is held down 4below the :preferred opera-ting speed at medium loads. Furthermore, the generator has a. tendency to unload :and permit the fengine to overspeed at .high currents.

In `order to correct the foregoing undesirable characteristics of the engine and ygenerator, .automatic regulation of the engine Ispeed is obtained by controlling the excitation of the generator in :accordance with operating :characteristics of the generator.. As shown by the curves -a, b, and c in Fig. 4, the engine speed may `be controlled by varying the excitation Aof the generator. In Fig. 4, the curve a represents the engine speed for minimum excitation of fa .particular machine. The curve b shows the speed for medium excitation, and :the curve c for maximum excitation. Thus, it will f'be lseen that "the speed of the eng-ine can be veither increased or decreased vby changing the excitation at the desired times.

in the system shown in Fig. 1, a, plurality of relays RI, R2, R3, and R4, which are .responsive to the generator amature current, are utilized for adusting the external resistance in the shunt field circuit Vof the generator il in accordance with `the .loa-d currents. Since the conventional engine 4speed curve has a reversed bend, :as shown in Fig. 3, it is necessary to set one-half of the series current relays to operate their contact members to shunt resistance out of the generator iield circuit in a predetermined order on heavy currents to prevent the generator from unloading and the engine overspeeding at high current values. The remaining one-half of the current responsive relays are set to close their contact members on low currents, thereby shunting the resistance out of the shunt elcl circuit to cause the generator to take load and decrease the engine speed at W current values.

Therefore,.in the particular embodiment of the invention shown, the relays RI and R2 have normally closed contact members which shunt resistors ZI, and 22, respectively, from the circuit for the shunt field Winding I5. The relays R3 and R4 have normally open contact members which are closed to shunt the resistors 2I and 22 from the iield winding circuit when the relays are energized by predetermined currents.Y Additional resistors 23 and 24 may be provided in the eld Winding circuit for adjusting the iield current.

By Way of illustration, it may be assumed that the relay RI is adjusted to open its contact members at 300 amperes which is approximately the current at Which the engine has a tendency to drop below the normal operating speed of 1800 R. P. M., as shown by the curves in Fig. 3. Therefore, the engine speed may be held at approximately 1800 R. P. M., when the generator is delivering from 300 to 400 amperes, by opening the contact members oi the relay RI to insert the resistor 2l in the eld Winding circuit and causing the load taken by the generator to decrease. Likewise, the relay R2 may be adjusted toV open its contact members at 400 amperes to insert the resistor 22 in the field Winding circuit, thereby further decreasing the load taken by the generator II which enables the engine to maintain its normal operating speed.

In the event that the generator current increases to 500 amperes, at which point the generator has a tendency to unload and permit the engine speed to increase, as shown by the curve in Fig. 3, the relay R3 is operated to close its contact members, thereby shunting the resistor 2| from the field Winding circuit which increases the excitation on the generator, causing it to take additional load to hold the engine at its normal speed. In a similar manner, the relay R4 may be set to close its contact members at 600 amperes to shunt the resistor 22 from the field Winding circuit to increase further the load taken by the generator. l

In this manner, the excitation of the generator II may be so controlled by the current responsive relays that the engine speed will be held approximately normal, as shown by the curve in Fig. 3 which represents the characteristics of an engine having speed control relays of a type herein disclosed. Thus the relays RI, R2, R3, R4 function to control the generator excitation in accordance With the load current and are so operated that the excitation is increased When the engine has a tendency to overspeed and is decreased when the engine is operating below its normal speed, thereby so controlling the load on the engine that it can maintain its normal operating speed. As explained hereinbefore, the relay V, which is responsive to the generator potential, is utilized to increase the excitation in order to cause the generator to build up its potential more quickly When the engine is being accelerated.

In the modification of the invention shown in Fig. 2, in which like parts are designated by the same reference characters as in Fig. 1, the gen'- erator Il is provided with a separately excited iield winding 25 in addition to the shunt eld Winding I5. The eld winding 25 is energized from the battery I6, and a rheostat 2B may be utilized to adjust the current supplied by the battery I6.

The curves in Fig. 4 illustrate the variation in the speed and volts of a typical engine-driven generator when the ampere output is varied. Thus, the curves a and a show the variation in speed and voltage with a minimum amount of excitation; the curves b and b illustrate the operation with a medium amount of excitation, and the curves c and c' are :for maximum excitation of the generator. y

It will be noted that the voltage decreases With an increase in the armature current of the generator. and that the speed of the engine decreases for medium amounts of current, but increases at relatively high currents. The increase in engine speed results from the decrease in the terminal voltage of the machine, which is caused by the armature reaction and increased resistance drop at high currents, thereby actually decreasing the total power output of the generator which decreases the load on the engine and permits its speed to increase.

In the system shown in Fig. 2, the excitation of the machine is controlled by a relay El which is responsive to the generator voltage, and an additional relay E having a potential coil E2, also responsive to the generator voltage, and a current coil I2 which is responsive to the generator current. The relay EI is provided vvith contact members EI I, which discon nect the battery I6 from the eld winding 25, and additional contact members E12, which shunt a resistor 21 fromk the circuit for the shunt field Winding I5. The relay E is provided with contact members E2! which also shunt the resistor 21 from the circuit for the eld Winding I5. An adjustable rheostat 28 is provided for manual adjustment of the currentin the iield Winding I5.

Referring to the curves in Fig. 4, andV assuming Vthat the machines are operated at heavy currents on the curves c and c', which represent maximum excitation conditions, the relay El is operated when the voltage O is reached to open its contact members EII to disconnect the battery I6 from the eld Winding 25. The contact members EIZ are also opened at this time to insert the resistor 21 in the circuit for the field winding I5, thereby reducing the excitation on the generator to its minimum value and causing the machines vto operate on the curves a and a, as shown by the heavy lines on the curves. VWhen the voltage P is reached as a result of the current being reduced to the value M, the coil E2 overcomes the magnetic effect of the coil I2 on the relay E and closes the contact members EZI, thereby shunting the resistor 21 from the circuit for the iield winding I5 and causing the machines to operate on the curves b and b' until a speed is attained at which the governor functions to control tle engine speed.

It Will be seen that the resultant engine speed over the operating range is much more constant than if the machines were operated on any one value of eld excitation. and that in this manner the engine speed may be held approximately constant throughout the operating range. It should be noted that the changes in speed and voltage in actual operation Will not be as abrupt as indicated by the heavy line, since the inertia of the rotating parts and the magnetic inertia of the shunt and battery excited elds tends to smooth out the changes in the characteristics of the machines.

From the foregoing description, it is apparent that We have devised a system which provides for regulating the engine speed throughout the operating limits of equipment of the type shown and improves the overall performance of Diesel or gas-electric drive equipment, since the engine speed is so controlled that it produces its maximum output over the load range of the equipment. Furthermore, the systems herein described are relatively simple and only require the use of relays of a standard design, Well-known in the electrical art. The present Systems do not require the use of additional auxiliary machines for regulating the speed oi the power machines utilized in the system.

Since numerous changes may be made in the above described construction and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all matter contained in the foregoing description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

We claim as our invention:

1. In a control system, in combination, a motor, a generator for supplying current to the motor, an engine for driving the generator, means for exciting the generator, a resistor for controlling the generator excitation current and relay means responsive to operating characteristics of the generator for alternately shunting said resistor, thereby varying the generator excitation to regulate the engine speed.

2l. In a control system, in combination, a motor, a generator for supplying current to the motor, an engine for driving the generator, means for exciting the generator, a resistor for controlling the generator excitation current and a pair of relays responsive to operating characteristics of the generator for alternately shunting said resistor, thereby varying the generator excitation to regulate the engine speed.

3. In a control system, in combination, a motor, a generator for supplying current to the motor, an engine for driving the generator, means for exciting the generator, a resistor for controlling the generator excitation current and a pair of relays disposed to operate in sequential relation to alternately shunt said resistor to vary the generator excitation, thereby regulating the engine speed.

4. In a control system, in combination, a motor, a generator for supplying current to the motor, an engine for driving the generator, means for exciting the generator, a resistor for controlling the generator excitation current, and relay means responsive to the generator current and voltage for alternately shunting said resistor, thereby varying the generator excitation to regulate the engine speed.

5. In a control system, in combination, a motor, a generator lor supplying current to the motor, an engine for driving the generator, means for exciting the generator, and a plurality of relays responsive to the generator current and operable in a predetermined sequence for alternately increasing and decreasing the generator excitation to regulate the engine speed.

6. In a control system, in combination, a motor, a generator for supplying current to the motor, an engine for driving the generator, means for exciting the generator, and a plurality of relays responsive to different values of generator current for alternately increasing and decreasing the generator excitation to regulate the engine speed.

7. In a control system, in combination, a motor, a generator for supplying current to the motor, an engine for driving the generator', means for exciting the generator, and a plurality of relays responsive to the generator voltage and operable in a predetermined sequence for alternately increasing and decreasing the generator excitation to regulate the engine speed.

8. In a control system, in combination, a motor, a generator for supplying current to the motor, an engine for driving the generator, means for exciting the generator, and a plurality of relays responsive to different values of generator potential for alternately increasing and decreasing the generator excitation to regulate the engine speed.

9. In a control system, in combination, a motor, a generator for supplying current to the motor, an engine for driving the generator, means energized by the generator for exciting the generator, an additional source of excitation for the generator, and relay means responsive to the current and the potential of the generator for alternately increasing and decreasing the total excitation supplied by said self-excited means and said additional source to regulate the engine speed.

BASCUM O. AUSTIN. CLARENCE A. ATWELL. 

